Rotary dryers have long been used in the dry rendering of animal fats and similar material. One such dryer is shown in U.S. Pat. No. 3,800,865 issued to Onarheim et al., and entitled "Heat Exchangers". The Onarheim dryer comprises a sealable cooking vessel having a multivaned heat transfer rotor centrally mounted therewithin. Powered rotation of the rotor during the rendering operation serves to agitate the material contained in the vessel for improved heat transfer efficiency from the rotor.
Another dryer suitable for dry rendering is disclosed in U.S. Pat. No. 3,777,810, issued to Phillips and entitled "Dryer". In the Phillips dryer, the disc-like annular vanes on the heat transfer rotor are each comprised of concentric, interconnected, toroidal chambers. The particular shape of the vanes in the Phillips dryer allows thin-wall construction of the vanes for improved heat transfer to the material in the vessel. Another rotary dryer, disclosed in Onarheim, U.S. Pat. No. 3,769,900, includes a jacketed vessel for additional heat transfer in cooperation with the heat transfer rotor.
Though the aforementioned dryers are suited for conventional dry rendering operations, they are not particularly heat efficient, they require a relatively long residence time which may be detrimental to the resultant protein products, and the ones of them which are capable of processing at high rates (more than 10,000 pounds per hour) require a substantial amount of floor space.